[XviD-devel] XVid Scene Detection Algorithm

[Christoph Lampert]

Hi Stefaan,

On Sun, 16 Nov 2003, Stefaan Moens wrote:
> I'm currently working on a thesis about scene detection in video.

Fine. What kind of thesis? 
I had a look at shot boundary detection (in particular fades) a while ago.
I would be interesting to stay in contact. 

> Since I read that in XVid there 's also a scene detection present, I
> wonder what kind of algoritm it is...

XVID only detects cuts, not fades/dissolves etc. When a cut is detected, 
a keyframe (I-VOP) is used instead of a predicted frame (P-VOP, B-VOP). 

The detection is rather simple motion based: The usual motion estimation
is performed, for every macroblock (16x16) a motion vector is
determined. If the match is too bad (absolute error larger than a
threshold), the block is marked as INTRA. If more than half of the
macroblocks of a frame are INTRA, the frame is classified at a cut. 

I found this more reliable than histogram or edge-based decision, and 
in encoding, motion estimation has to be done anyway, so the decision is
more or less for free. 


> Can anyone tell me? And is it freely available?

XVID is available as Free Software under GPL. The algorithm is
"trivial" and has been described very often in literature, so I guess and
hope, it's also free of IP rights. 

gruel